Method for inhibition of sorbate-induced brown discolorations in cosmetic compositions and foodstuffs, and color-stabilized formulations containing sorbate preservative.
The invention relates to a method for the preparation of color-stabilized cosmetic compositions and foodstuffs containing sorbate preservative and to these compositions themselves.
Sorbic acid (2,4-hexadienoic acid) and its salts, in particular the readily water-soluble potassium salt, have been used worldwide for many years for preserving food-stuffs. Sorbic acid is an unsaturated fatty acid which is distinguished by particular physiological tolerability. Sorbic acid is metabolized in the human body analogously to a fatty acid, is not accumulated and is classified as safe by the scientific advisory committees of the World Health Organization and of the European Union. The ADI (acceptable daily intake) value specified for sorbic acid by both committees, which can be rated as a measure of the physiological acceptability of foodstuff additives, is 0 to 25 mg/kg of body weight and day and is therefore by far the highest ADI value of all preservatives. Sorbic acid and sorbates are regarded as non-allergenic and are therefore also not mentioned in any of the known allergy databanks (for example Leatherhead Food Tolerance Data-banks Project).
The activity of sorbic acid is directed, above all, against yeasts and molds, and to a somewhat lesser extent against bacteria. The activity of sorbic acid depends on the non-dissociated content and therefore on the pH of the goods to be preserved. Because of the high pH of 4.76, sorbic acid is also suitable for preserving weakly acid goods (to pH 6.5), in contrast to other preservatives based on organic acids.
In the solid form, sorbic acid and sorbates are stable. In aqueous solution, in foodstuffs and in cosmetic compositions, however, sorbic acid is subject to oxidative influences. In particular, aldehydes and ketones, which may be the cause of off-flavors, can be formed by oxidative cleavage of the double bonds. Polymerization products of these aldehydes, like the reaction products of these aldehydes with amino acids or other primary and secondary amino groups, can also be responsible for color changes, in particular browning reactions. Such products are called Maillard products and in many cases are responsible for color changes in cosmetic compositions and foodstuffs.
The mechanism of oxidation of sorbic acid and corresponding stabilization measures have in many cases been the subject of scientific studies (Arya, S. (1980); Stability of sorbic acid in aqueous solutions. Journal Agric. Food Chem. 28, 1246-1249; Arya. S., Thakur, B. (1988): Degradation products of sorbic acid in aqueous solutions. Food Chem. 29, 41-49; Ledward, D. (1990); Stability of sorbic acid in intermediate moisture systems. Food Add. Contam. 7, 677-683; Merciadez, M., Mohammed, K., Maniere, F. (1992): Stabilized sorbic acid or salts therefore. U.S. Pat. No. 966,246, Oct. 10, 1992; Thakur, B., Singh, R., Arya, S. (1994): Chemistry of sorbatesxe2x80x94a basic perspective. Food Rev. Intern. 10, 71-91). In the context of the abovementioned studies, attempts have been made in some cases to reduce the sorbate-induced brown discolorations and odor changes described for foodstuffs by addition of metal ions (in particular manganese) in a concentration range of 0.1-5 ppm. In addition, color stabilization of, for example, sweetener solutions also by salts of copper, zinc and cobalt has been described. The addition of these metals, which also all have a pro-oxidative action depending on the concentration, to foodstuffs seems unacceptable physiologically. The same applies to cosmetic compositions. There therefore also continues to be the need to prevent sorbate-induced brown discolorations both in foodstuffs and in cosmetic compositions.
On the basis of their good activity against micro-organisms which spoil cosmetics and their particular skin tolerability and physiological safety, sorbic acid has recently been employed increasingly for preservation of cosmetic compositions. Sorbates are the preservatives of choice for cosmetic compositions since:
they act to a particular extent against micro-organisms which spoil cosmetics (for example Pseudomonas aeruginosa)
they prevent the formation of mycotoxins in cosmetic compositions
they have a good skin and mucosa tolerability
they do not irritate the skin
they are not phototoxic
they cause no ecological problems (water pollution class 0)
On the basis of these excellent physiological data, sorbic acid has been classified as xe2x80x9csafexe2x80x9d by the CIR Expert Panel, and is approved worldwide for use in cosmetic compositions.
The technological advantages of the use of sorbate in cosmetic compositions are the following:
protection from microbial contamination during storage and use
good compatibility with the raw materials of cosmetics
no inactivation by the contents of cosmetics
xe2x80x9csynergisticxe2x80x9d effects with other preservatives in cosmetics
high activity at pH values relevant to cosmetics
because of the favorable partition coefficient (the microbiological sensitive aqueous phase remains), particularly suitable for preserving oil-in-water emulsions
no loss of action by reaction with packaging materials
On the basis of these excellent technological properties, sorbates are employed in all cosmetic compositions (for example shampoos, shower gel, body lotion, sunscreen preparations, cleansing milk, facial lotion, self-tanning compositions, decorative cosmetics, oral hygiene products and moist tissues or moist toilet paper). However, it is known from the literature that precisely in cosmetic compositions which are stored for a relatively long time, are exposed to an oxidative influence and comprise amino components, sorbate-induced brown discolorations still lead to problems (Domsch, A. (1994): Die kosmetischen Prxc3xa4parate [Cosmetic Preparations], volume 2: Wassrige und tensidhaltige Formulierungen [Aqueous and surfactant-containing formulations], 4th edition, page .329, Augsburg: Verlag fur die chemische Industrie). The protective measure implemented most frequently to date is the co-use of complexing agents (EDTA or citrates), which slow down sorbate-induced brown discolorations by complexing pro-oxidative metal ions. Modifications to the perfuming are a second possibility. A delay in sorbate-induced brown discolorations can be achieved by both measures. However, the problem mentioned still remains for clear formulations in clear plastic bottles (a formulation which is currently used very often) in particular. Since the brown discolorations described are temperature-dependent, this applies in particular to cosmetic compositions exported to tropical countries.
Since sorbates, because of their antimicrobial activity, can also be used as active compounds in mouthwashes, toothpastes and cleaning compositions for dentures and these products are often available as clear formulations, the use of allantoin as an active compound (anti-inflammatory, analgesic) and an inhibitor of brown discolorations caused by sorbate in oral hygiene compositions is described (Hirohata, H., Ozawa, T. (1993): Composition for dental use. JP 5-339135). However, since they generally comprise no amino components which accelerate discoloration, oral hygiene compositions do not make too high a demand on the browning-inhibiting substance.
Since degradation products of sorbic acid formed oxidatively can react to a particular extent with foodstuff constituents of high nutritional physiology value, such as amino acids, protection of sorbic acid against oxidative changes is also of considerable relevance in nutritional physiology. Studies which describe a reactivity of sorbic acid degradation products with amino acids such as lysine or glutamic acid are available (Ledward, A. D: (1990): Stability of sorbic acid in intermediate moisture systems, Food Add. Contam. 7, 677-683).
There was thus a need for a method which enables cosmetic compositions and foodstuffs to be preserved with sorbic acid without brown colorations or sensorially relevant changes occurring.
This object is achieved by a method for visual and sensorial stabilization of foodstuffs and cosmetic compositions containing sorbate preservative, which comprises adding allantoin or allantoin and citrates to these products as browning inhibitors.
The foodstuffs and cosmetic compositions containing sorbate preservative can comprise the preservative here both in the form of free sorbic acid and as physiologically acceptable salts thereof, such as, for example, potassium sorbate or calcium sorbate. The sorbate concentrations used, calculated as sorbic acid, for foodstuffs and cosmetic compositions are in general between 0.005% and 5%.
Surprisingly, sorbate-induced discolorations and odor changes in all types of cosmetic compositions can be minimized drastically by addition of allantoin, an active compound often used in cosmetics because of its anti-inflammatory, keratinolytic and wound-healing properties. If citrates (for example citric acid or disodium citrate) are additionally employed as complexing agents, sorbate-induced discolorations can be prevented virtually entirely. The usual use concentrations of sorbates in cosmetic compositions, calculated as sorbic acid, are summarized in the following table. If other preservatives for cosmetics are co-used, the concentrations are correspondingly lower.
Allantoin is advantageously employed in amounts of the order of 0.01 to 10% by weight, in particular 0.05 to 5% by weight, preferably 0.1 to 3% by weight, particularly preferably 0.2 to 2% by weight. For citrates, an amount of the order of 0.05 to 5% by weight, in particular 0.1 to 3% by weight, preferably 0.2 to 2% by weight and particularly preferably 0.2 to 1% by weight is recommended. Good results are achieved if the allantoin concentrations, compared with the sorbate concentrations used, are 30 to 200% by weight, in particular 40 to 150% by weight and preferably 50 to 100% by weight. Corresponding higher allantoin concentrations can be chosen for formulations which are particularly susceptible to browning. Citrates should be used in the same concentration on a percentage basis as the sorbates. If citrates are used for the purpose of pH regulation, higher concentrations can also be employed.
The invention furthermore relates to foodstuffs and cosmetic compositions containing sorbate preservative, which comprise allantoin or allantoin and citrates.
The foodstuffs and cosmetic compositions which are of particular interest here are those which comprise between 0.005 and 5% of sorbate, in particular between 0.5 and 2% by weight, preferably between 0.1 and 0.8% by weight and particularly preferably between 0.15 and 0.4% by weight (calculated as sorbic acid) and between 0.001 and 10% by weight, in particularly between 0.1 and 3% by weight, preferably between 0.2 and 2% by weight and particularly preferably between 0.2 and 1% by weight of allantoin, or between 0.001 and 10% by weight of allantoin and between 0.05 and 5% by weight, in particularly between 40 and 150% by weight and preferably between 50 and 100% by weight of citrate.
The fact that allantoin, although it contains three secondary amino groups and one primary amino group, is capable of preventing sorbate-induced discolorations in cosmetic compositions and foodstuffs seems particularly surprising. Amino groups precisely are regarded as an additional xe2x80x9crisk factorxe2x80x9d with respect to sorbate-induced discolorations. Furthermore, no findings that allantoin has a noticeable antioxidative potential (for example quenching of singlet oxygen or free radicals of oxygen or hydroxyl) are available from the literature. Rather, it seems that the reaction products between the sorbate degradation products and allantoin surprisingly are not colored and cause no sensorial problems. Considering the intrinsic coloration of reaction products between sorbate degradation products and amino acids, this property (colorlessness) of sorbate-allantoin adducts is particularly remarkable.
Tables 2 and 3 show the protective action of allantoin and citrates and the corresponding synergisms in aqueous solutions.
As expected, with the addition of an amino acid, for example alanine, the discoloration of the control (without allantoin and citrates) is accelerated, while the protective action of allantoin and the synergistic mixture of allantoin and citrate is documented again (see Table 4).